The present invention relates to an apparatus and method for detecting a hovering object using inherently intrinsic capacitance compensation, and an apparatus and method for detecting a force input using inherently intrinsic capacitance compensation.
Object sensing methods currently used in touch screens mainly include a resistive type, a surface acoustic wave type, and a capacitive type. Capacitive touch screens can sense multiple touches, have excellent durability, visibility, etc., and thus are being employed as main input means of portable devices.
A capacitive touch screen recognizes a user input by sensing a change in the quantity of electric charge in capacitive sensors on a touch screen panel caused by a user intervention. According to charge accumulation methods, capacitive touch screens are classified into a self-capacitive type and a mutual-capacitive type. In a self-capacitance touch screen, each capacitive sensor constitutes one conductor and forms an electric charge surface together with a reference ground outside the touch screen panel, but in a mutual-capacitance touch screen, two conductors on the touch screen panel mutually form an electric charge surface and function as one capacitive sensor.
A general self-capacitance touch screen uses an X-Y orthogonal arrangement of conductors. In this case, each capacitive sensor functions as a line sensor, and thus only one piece of X-sensing information and one piece of Y-sensing information are respectively provided by an X-line sensor group and a Y-line sensor group every time the touch screen is scanned. Therefore, the general self-capacitance touch screen can sense and track a single touch but cannot support multiple touches. A mutual-capacitance touch screen also uses an X-Y orthogonal arrangement of conductors. However, the mutual-capacitance touch screen differs from the self-capacitance touch sensor in that capacitive sensors are each placed at intersections of conductors in the form of grid sensors, and responses of all grid sensors are independently sensed when a user input on the touch screen is detected. Since grid sensors each correspond to different X-Y coordinates and provide independent responses, the mutual-capacitance touch screen can sense and track multiple touches of a user by extracting user input information from a set of X-Y sensing information provided by a set of X-Y grid sensors.
A general mutual-capacitance touch screen panel has the following configuration of conductors and sensing method. First electrodes formed of conductors extending in any one direction and second electrodes formed of conductors extending in a direction perpendicular to the first electrodes form mutual-capacitive sensors in which a dielectric material between the two electrodes is used as a medium. A capacitance C of the sensor is defined as C=∈×A/d where the distance between the two electrodes is d, the area of an electric charge surface is a, and an equivalent dielectric constant of all dielectric materials between electric charge surfaces is ∈. The capacitance C has a relationship of Q=CV with an amount Q of electric charges accumulated on the sensor and an electric potential difference (voltage) V applied to two electrodes/electric charge surfaces. When a user approaches a sensor, interference to an electric field formed between the two electrodes occurs to prevent a part of electric charges from being accumulated on the sensor. Therefore, an amount of electric charges accumulated on the sensor is reduced, and consequently the capacitance is reduced. This may be understood as a change in the capacitance caused by a change in an equivalent dielectric constant between the electric charge surfaces due to the user's approach to the sensor, but the actual physical phenomenon is that a part of the electric field between the electric charge surfaces is shunted due to the user's approach so that the amount of electric charge accumulated on the surfaces are reduced. When applying an alternating current (AC) waveform to one electric charge surface of the sensor by connecting an AC voltage source to the first electrode, variation ΔQ of ΔQ=ΔCV in the amount of electric charge with respect to the capacitance C which varies according to a degree of the user's approach to the sensor occurs, and the charge variation is converted into a current or a voltage by a read-out circuit connected to the second electrode. Such converted information is generally subjected to signal processing operations such as noise filtering, demodulation, digital conversion, accumulation, etc. and used in a coordinate tracking algorithm and a gesture recognition algorithm.
An existing touch detection device for detecting a single touch was developed to detect multiple touches, but could only detect an object coming in touch with the device surface. To overcome this limitation, a touch detection device has become possible to detect an object which does not come in touch with but hovers over the device surface or to detect through a touch panel a force input provided by a user pressing the touch panel, or has been developed to additionally include a force sensing device in the touch panel.
According to a mutual-capacitive touch sensing method, an object touches and absorbs an electric field formed between a driving electrode and a sensing electrode, and a resultant change is detected. Therefore, electric fields are intensively formed on a surface of a touch detection device, and it is difficult to detect an object which does not come in touch with but hovers over the surface of the touch detection device using the mutual-capacitive touch sensing method.
As a method of detecting a hovering object, a self-capacitive method of detecting a capacitance between one electrode of a touch panel and a hovering object is preferable. However, a change in the capacitance between a driving electrode and the hovering object caused by movement of the hovering object is 1/10 to 1/100 of a change in the capacitance which is required to be detected in the mutual-capacitive method. Also, with reductions in the size and the thickness of a touch panel, a resistance value of electrodes and capacitance values of capacitors, such as a parasitic capacitance between an electrode and the ground, a parasitic capacitance between electrodes, etc., intrinsically inherent in the panel have become hundreds of times to tens of thousands of times of a capacitance value formed by a hovering object. Therefore, according to related art, it is difficult to overcome the influence of intrinsically inherent capacitance and detect a hovering object.
Also, in a method of detecting an input provided by a user applying force to a force sensing device, a change in a capacitance value may be used. In an existing force sensing device, intrinsically inherent capacitance values of capacitors, such as a parasitic capacitance between an electrode and the ground, a parasitic capacitance between electrodes, etc., are larger than a change in capacitance caused by a force input provided by a user. Along with a trend toward reductions in the size and the thickness of an electronic device, a parasitic capacitance value and a capacitance value of a force sensing capacitor are continually increasing, but a change in capacitance caused when a user applies force to a touch panel is decreasing. Therefore, it is getting more difficult to detect an input of a user with accuracy and sensitivity for ensuring reliability.